backend/headless: add wlr_headless_backend_create_with_renderer

This allows one to create a headless backend with an existing renderer.

backend/headless/backend.c

@@ -62,7 +62,9 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 	wlr_signal_emit_safe(&wlr_backend->events.destroy, backend);
 
 	wlr_renderer_destroy(backend->renderer);
-	wlr_egl_finish(&backend->egl);
+	if (backend->egl == &backend->priv_egl) {
+		wlr_egl_finish(&backend->priv_egl);
+	}
 	free(backend);
 }
 
@@ -85,41 +87,15 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
 	backend_destroy(&backend->backend);
 }
 
-struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
+static bool backend_init(struct wlr_headless_backend *backend,
-		wlr_renderer_create_func_t create_renderer_func) {
+		struct wl_display *display, struct wlr_renderer *renderer) {
-	wlr_log(WLR_INFO, "Creating headless backend");
-
-	struct wlr_headless_backend *backend =
-		calloc(1, sizeof(struct wlr_headless_backend));
-	if (!backend) {
-		wlr_log(WLR_ERROR, "Failed to allocate wlr_headless_backend");
-		return NULL;
-	}
 	wlr_backend_init(&backend->backend, &backend_impl);
 	backend->display = display;
 	wl_list_init(&backend->outputs);
 	wl_list_init(&backend->input_devices);
 
-	static const EGLint config_attribs[] = {
+	backend->renderer = renderer;
-		EGL_SURFACE_TYPE, 0,
+	backend->egl = wlr_gles2_renderer_get_egl(renderer);
-		EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
-		EGL_BLUE_SIZE, 1,
-		EGL_GREEN_SIZE, 1,
-		EGL_RED_SIZE, 1,
-		EGL_NONE,
-	};
-
-	if (!create_renderer_func) {
-		create_renderer_func = wlr_renderer_autocreate;
-	}
-
-	backend->renderer = create_renderer_func(&backend->egl,
-		EGL_PLATFORM_SURFACELESS_MESA, EGL_DEFAULT_DISPLAY,
-		(EGLint*)config_attribs, 0);
-	if (!backend->renderer) {
-		wlr_log(WLR_ERROR, "Failed to create renderer");
-		goto error_backend;
-	}
 
 	if (wlr_gles2_renderer_check_ext(backend->renderer, "GL_OES_rgb8_rgba8") ||
 			wlr_gles2_renderer_check_ext(backend->renderer,
@@ -136,13 +112,68 @@ struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 	backend->display_destroy.notify = handle_display_destroy;
 	wl_display_add_destroy_listener(display, &backend->display_destroy);
 
-	return &backend->backend;
+	return true;
+}
 
-error_renderer:
+struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
-	wlr_renderer_destroy(backend->renderer);
+		wlr_renderer_create_func_t create_renderer_func) {
-error_backend:
+	wlr_log(WLR_INFO, "Creating headless backend");
-	free(backend);
+
-	return NULL;
+	struct wlr_headless_backend *backend =
+		calloc(1, sizeof(struct wlr_headless_backend));
+	if (!backend) {
+		wlr_log(WLR_ERROR, "Failed to allocate wlr_headless_backend");
+		return NULL;
+	}
+
+	static const EGLint config_attribs[] = {
+		EGL_SURFACE_TYPE, 0,
+		EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
+		EGL_BLUE_SIZE, 1,
+		EGL_GREEN_SIZE, 1,
+		EGL_RED_SIZE, 1,
+		EGL_NONE,
+	};
+
+	if (!create_renderer_func) {
+		create_renderer_func = wlr_renderer_autocreate;
+	}
+
+	struct wlr_renderer *renderer = create_renderer_func(&backend->priv_egl,
+		EGL_PLATFORM_SURFACELESS_MESA, EGL_DEFAULT_DISPLAY,
+		(EGLint*)config_attribs, 0);
+	if (!renderer) {
+		wlr_log(WLR_ERROR, "Failed to create renderer");
+		free(backend);
+		return NULL;
+	}
+
+	if (!backend_init(backend, display, renderer)) {
+		wlr_renderer_destroy(backend->renderer);
+		free(backend);
+		return NULL;
+	}
+
+	return &backend->backend;
+}
+
+struct wlr_backend *wlr_headless_backend_create_with_renderer(
+		struct wl_display *display, struct wlr_renderer *renderer) {
+	wlr_log(WLR_INFO, "Creating headless backend");
+
+	struct wlr_headless_backend *backend =
+		calloc(1, sizeof(struct wlr_headless_backend));
+	if (!backend) {
+		wlr_log(WLR_ERROR, "Failed to allocate wlr_headless_backend");
+		return NULL;
+	}
+
+	if (!backend_init(backend, display, renderer)) {
+		free(backend);
+		return NULL;
+	}
+
+	return &backend->backend;
 }
 
 bool wlr_backend_is_headless(struct wlr_backend *backend) {

backend/headless/output.c

@@ -16,7 +16,7 @@ static struct wlr_headless_output *headless_output_from_output(
 
 static bool create_fbo(struct wlr_headless_output *output,
 		unsigned int width, unsigned int height) {
-	if (!wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL)) {
+	if (!wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL)) {
 		return false;
 	}
 
@@ -46,7 +46,7 @@ static bool create_fbo(struct wlr_headless_output *output,
 }
 
 static void destroy_fbo(struct wlr_headless_output *output) {
-	if (!wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL)) {
+	if (!wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL)) {
 		return;
 	}
 
@@ -82,7 +82,7 @@ static bool output_attach_render(struct wlr_output *wlr_output,
 	struct wlr_headless_output *output =
 		headless_output_from_output(wlr_output);
 
-	if (!wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL)) {
+	if (!wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL)) {
 		return false;
 	}
 
@@ -129,7 +129,7 @@ static bool output_commit(struct wlr_output *wlr_output) {
 		wlr_output_send_present(wlr_output, NULL);
 	}
 
-	wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL);
+	wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL);
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 
 	return true;
@@ -138,7 +138,7 @@ static bool output_commit(struct wlr_output *wlr_output) {
 static void output_rollback(struct wlr_output *wlr_output) {
 	struct wlr_headless_output *output =
 		headless_output_from_output(wlr_output);
-	wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL);
+	wlr_egl_make_current(output->backend->egl, EGL_NO_SURFACE, NULL);
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 }
 

include/backend/headless.h

@@ -9,7 +9,8 @@
 
 struct wlr_headless_backend {
 	struct wlr_backend backend;
-	struct wlr_egl egl;
+	struct wlr_egl priv_egl; // may be uninitialized
+	struct wlr_egl *egl;
 	struct wlr_renderer *renderer;
 	struct wl_display *display;
 	struct wl_list outputs;

include/wlr/backend/headless.h

@@ -19,6 +19,11 @@
  */
 struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 	wlr_renderer_create_func_t create_renderer_func);
+/**
+ * Creates a headless backend with an existing renderer.
+ */
+struct wlr_backend *wlr_headless_backend_create_with_renderer(
+	struct wl_display *display, struct wlr_renderer *renderer);
 /**
  * Create a new headless output backed by an in-memory EGL framebuffer. You can
  * read pixels from this framebuffer via wlr_renderer_read_pixels but it is